First you should have a DynDNS provider like dynv6.com that can resolve a name to the external IPv6 address of your network (to make this a bit easier).
IPv6 adress should be this one if you have a FritzBox:
Then make a port share to the IPv6 adress of your proxy server:
After that every proxy should be able to resolve the incoming requests and forward them to other internal addresses (no matter if IPv6 or IPv4).
I just tested it with my Traefik Docker installation and it worked so far with entering the external IPv6 address.
Fortunately I don’t have to use it, because I am one of the lucky ones who still have a real dual-stack connection (without Lite) at Unitymedia. 